Xerophytes and hydrophytes

What is a xerophyte

A species of plant that has adaptations to survive in an environment with little water

What are some examples of xerophytes

• Conifers

• Cacti

• Marram grass

How are the might xerophytes stomata be adapted for survival

• Sunken stomata reduces air movement creating humid microenvironment so transpiration reduces, some even have micro hairs

• Reduced number of stomata helps reduce transpiration loss

How might the leaves of xerophytes be adapted for survival

• Reduced number of leaves lower SA:V ratio minimising water loss through transpiration, conifer leaves reduced to needles

• Hairy leaves creates humid microclimate around leaf reducing water vapour potential gradient minimising loss of water by transpiration

• Leaf loss when water unavailable and trunk and branches turn green to photosynthesise with minimal water loss

• Curled leaves, confines all stomata withing microenvironment of humid air, reducing diffusion of water vapour from stomata

How are xerophytes cuticles adapted for survival

Thick waxy helps minimise water loss as 10% water loss by transpiration through the cuticle

What are succulents

Xerophytes which store water in specialised parenchyma tissue in roots and stems. Water stored plentifully and used in times of drought, have swollen appearance. An example is the aloe vera

How might the roots of xerophytes be adaptedfor survival

Long tap roots which grow deep into ground. Widespread shallow roots with large SA to absorb any available water

Other ways xerophytes survive

• Lose leaves and become dormant

• Die leaving seed behind which will only germinate when there is enough rain water

• Survive as storage organs

• Few plants become turgid and green and recover when it rains again

What are hydrophytes

Plants which live in water and are specially adapted to cope with growing in water or permanently saturate soil

What are some examples of hydrophytes

• Marginals

• Duckweeds

• Water cress

• Water lilies

How are hydrophytes cuticles adapted for survival

Very thin or no waxy cuticle as they do not need to conserve water as it is plenty

How are the stomata of hydrophytes adapted for survival

Maximising number of stomata maximises gaseous exchange. No loss of turgor as water always available. Stomata always open for gaseous exchange. Plants with floating leaves have stomata on upper leaf so in contact with air

How is the structure of a hydrophyte adapted for survival

• Reduced supporting structures as water supports leaves and flowers, also may have wide flat leaves to maximise light absorption

• Small roots as water can diffuse directly into stem and leaf tissue

• Large SA of stems and roots under water maximises area for photosynthesis and for oxygen to diffuse into submerged plants

• Air sacs enable leaves or flowers to float

• Aerenchyma, specialised parenchyma in leaves, stems and roots which form in normal parenchyma apoptosis so air spaces form. So stems and leave more buoyant, creates pathway for oxygen to tissues below water and helps plant to cope with anoxic conditions